The mind boggles - I'm trying to imagine a hedge in a tub, but I'll assume you mean you have a box plant in a pot and you want to clip it. Trim it over to keep it in shape 2 or 3 times a year, topdress with something like Growmore around now, removing a little of the compost from the top, add growmore, top off with extra compost, keep watered.

You and me both Bamboo.............

Bless you Bamboo. You always manage to answer even the most vaguest of questions...lol

Oh dear, dylandog, I seem to remember my stepmother saying to me when I was 14 "you've always got an answer..." (in exasperation, I might add, lol)